1. Field of the Invention
The invention generally relates to an illumination system and a projection apparatus, and more particularly, to an illumination system and a projection apparatus with higher light utilization efficiency.
2. Description of Related Art
Along with the progress of display technology, in terms of the light source employed by a projection apparatus, two kinds thereof have been launched. One kind of the projection apparatuses employs a ultra high pressure lamp (UHP lamp) emitting white light in association with a color wheel to sequentially generate red light, green light, and blue light, which makes the projection apparatus provide colorful image frames. The other kind of the projection apparatuses developed in recent years employs red light emitting diodes (LEDs), green LEDs, and blue LEDs as the light source thereof.
In a projection apparatus where red LEDs, green LEDs, and blue LEDs serve as the light source thereof, usually an X-mirror is used for combining light. For example, an X-mirror includes a red dichroic mirror and a blue dichroic mirror intersecting each other, so that a red light beam emitted from the red LEDs is reflected by the red dichroic mirror, a blue light beam emitted from the blue LEDs is reflected by the blue dichroic mirror, and a green light beam emitted from the green LEDs passes through the red dichroic mirror and the blue dichroic mirror. The X-mirror has different actions on the light beams of different colors, so that the red light beam, the green light beam, and the blue light beam respectively having different transmission directions are guided to a same direction. After the above-mentioned red light beam, green light beam, and blue light beam arrive at a digital micro-mirror device (DMD) in the projection apparatus and are acted by the DMD, desired color image frames are formed.
It should be noted that in an X-mirror, since a region where the red dichroic mirror and the blue dichroic mirror are cemented by each other (i.e., an intersecting region) is unable to normally guide the red light beam, the green light beam, and the blue light beam, so that a light loss is produced. In addition, when the light source is altered from the traditional UHP lamp to the LEDs, with respect to the sectional areas of the light beams emitted by the LEDs, the area of the above-mentioned cemented region gets larger to cause a light loss with a greater proportion. Besides, in a projection apparatus adopting an X-mirror, the red light beam, the green light beam, and the blue light beam are required to be incident upon the X-mirror from three different directions, which results in a low space utilization ratio for the components in the projection apparatus and in a bulky size of the projection apparatus itself.